What's Wrong With DTV? An overview.

Contributor

Out there, you might have noticed that the quality of some broadcast DTV, particularly some HDTV, ain't quite up to snuff. Lord knows Mario has.

This is particularly noticeable because, as we have known for some time, digital video and audio don't, as the expression goes, "degrade gracefully," as their analog counterparts do. Here's what Mario is talkin' about.

Assumin' NTSC video is of high quality when it is transmitted and no multipath situations are encountered, the primary quality-degradation mechanism experienced by the viewer is weak signal strength at the receiver. As the signal becomes weaker and weaker, the picture on the tube gets fuzzier and fuzzier, until eventually it just vanishes into the snow. For analog audio, just substitute the word "noise" for "snow."

Viewers have generally demonstrated a high tolerance for fuzzy NTSC pictures, largely because the fuzziness is just a random, incoherent degradation of the still-comprehensible images; no disturbing, visually unrelated artifacts like blocks are generated. Mario is here to tell you that the same cannot be said for digital pictures.

We all know about the digital "cliff effect," also known in the early days of DTV transmission experimentation as the "valley of death." In a nutshell, this may be expressed in this way: either ya get a perfect picture, or ya get no picture at all. Well, now that we are transmitting and viewing digital images daily, we know that this ain't necessarily the whole story.

We have experienced a passel of digital artifacts in received DTV pictures and we will experience a passel more.

DIGITAL DEGRADATION

One familiar digital artifact is caused by the old nemesis: weak signal strength. Valley of death notwithstanding, when the signal strength of an ATSC DTV transmission at the receiver becomes marginal, macroblock errors appear in the images. These are manifest as portions of the picture turning to garbage; garbage in rectilinear packages.

These errors can be large or small, ranging from a very short, thin horizontal rectangle to a substantial chunk of the picture. These artifacts come and go. At the extreme, the whole dadburn raster can turn into a pig's breakfast, resembling a screen full of shards of broken glass, before the signal disappears completely. This sort of degradation is not necessarily or typically the broadcaster's fault.

The other type of digital degradation Mario is seeing is caused by the broadcaster, particularly when the broadcaster attempts to pack 10 pounds into a 5-pound bag. The root cause of such degradation is the fact that a DTV signal is a stream of compressed digital data, and, as is the case with all digital data streams, the various components must share a finite amount of digital bandwidth. It's a mathematics game, and some play it better than others.

A broadcast television channel carries a data stream with a bandwidth of about 19.39 Mbps, into which all the compressed audio and video elements must fit. This works okay, for the most part, when a single HDTV signal is being transmitted on a channel. Usually.

We know that a broadcast HDTV signal is very highly compressed, and that the more motion the pictures contain, the more stress is placed on the encoding or compression device.

At the extreme, for example, in fast-moving sports and suchlike, a channel transmitting even a single HDTV signal can occasionally fall apart with compression artifacts. We can see portions of the image turn to square blocks momentarily as the encoder runs out of gas, and we can also see such blocks in a quick scene change or a fast fade-up from black or white. This is often called "tiling," and the appearance is much different from macroblock errors. The smaller the pixels, the smaller the blocks: SD tiles are larger than HD tiles.

We know fer sure, too, that 720p HDTV is considerably less stressful to the DTV encoder than is 1080i HDTV, for all those reasons we have heard before.

Mario's main point here has to do with what's goin' on out there with DTV broadcasting. For all the familiar financial reasons, broadcasters are taking advantage of the ability of their ATSC signals to carry multiple programs. Taking excessive advantage, in some cases.

Most, but not all, broadcast DTV signals carry an HDTV program, which may be called the "main channel." Many also carry one or more additional "subchannels," which can range from low-resolution, limited-motion weather channels, all the way up to a second network program. All these programs have to share the channel's19.39 Mbps bandwidth, and its encoding resources.

PACKING ATSC DATA STREAMS

It won't come as a complete surprise to discover that there is a limit to how much stuff can be packed into a single ATSC data stream. One real-life example is a station in a major market that packed one HDTV signal and three SD signals into a channel, a not uncommon practice.

This particular station did use 720p for the HD signal, but the total package was just too dang much for its container. When watching the HD signal random compression artifacts flashed through the images, the frequency of their appearance depending on what was going on in the programming in all the main and subchannels.

They often took the form of little blocks momentarily appearing in people's faces, outdoor scenes, etc. People's faces, for example, suddenly appeared to be behind screen doors. When this channel eventually dropped one of its subchannels, the situation improved, but did not entirely disappear.

Another real-life station in a much smaller market broadcasts a 1080i network program on its main channel, a whole other broadcast network in SD on its first subchannel, and an SD version of the HD main program on its second subchannel. Both the 1080i main channel and the first subchannel typically have a whole heap of tiling and sundry compression artifacts, and the first subchannel experiences occasional audio dropouts, not to mention serious lip-sync errors.

Methinks all this is not the best way to attract viewers. What can be done about it? Glad you asked.

Recent-generation encoders have improved greatly. At least one station in a major market, which primarily carries the signal of a broadcast network that broadcasts in 720p, is able, with state-of-the art encoders, to successfully broadcast two, count 'em two, 720p programs simultaneously.

The primary 720p signal is allocated more bits than the secondary one, and it looks right good, with only the occasional small bit of tiling to be seen. The secondary 720p program doesn't look as good, but it is adequate for the purpose, and it doesn't usually contain much fast motion. On the other hand, stations attempting to broadcast a 1080i signal and two full-resolution, full-motion SD signals, are probably kiddin' themselves.

Approaches to improving the broadcast DTV multicasting problem include selection of the most advantageous scanning formats, judicious allocation of the available bit budget, and use of state-of-the-art encoding devices. Like DTV receivers, succeeding generations of DTV encoders have steadily shown markedly improved performance.

Mario thinks there is a lesson here for economically beleaguered broadcast TV stations. Bad pictures are not the best way to attract viewers to broadcast television.

I agree 100%! If it doesn't fit, don't try shoving it in the bag. On the other hand, I do like quality (yes quality) sub-channels. But, at the moment the idea of channel sharing, at least until encoder technology gets up to snuff, is a bad idea.

But, why did they lose signals? Was it because signal strength dropped with the transition (that is possible), was it because they didn't have the right type of antenna, or was their antenna pointed in the wrong direction? I gained channels both because of subchannels and improved reception from Denver. I've seen some comments of people losing channels, which I'm sure was because their VHF antenna no longer received channels 2,4, and 6 (34,35, and 18 UHF). What I'm saying is a lot of this comes down to ignorance. Ignorance is fixable with education.

Of course there is also the sucky Low-VHF factor.

But, all in all your talking about a very small percentage of the population who had problems, and who would want to go back to analog.

Too bad Mario didn't do the research necessary to prove his assumption, that viewers care so much about video quality that they'll watch television so much more if the video was better that it would raise more revenue that the costs that it would incur. I see nothing in his work to support that implication. The vast majority of Americans couldn't tell the difference between 480i from a DVD and 1080i from a "perfect" HDTV broadcast. That's what's going to matter, not enthusiasts' purist perspective.

Contributor

Too bad Mario didn't do the research necessary to prove his assumption, that viewers care so much about video quality that they'll watch television so much more if the video was better that it would raise more revenue that the costs that it would incur. I see nothing in his work to support that implication. The vast majority of Americans couldn't tell the difference between 480i from a DVD and 1080i from a "perfect" HDTV broadcast. That's what's going to matter, not enthusiasts' purist perspective.

"Too bad Mario didn't do the research necessary to prove his assumption, that viewers care so much about video quality that they'll watch television so much more if the video was better that it would raise more revenue that the costs that it would incur".

How do you know he did not do his research? Are you the all knowing, all seeing self appointed messiah?

"The vast majority of Americans couldn't tell the difference between 480i from a DVD and 1080i from a "perfect" HDTV broadcast. That's what's going to matter, not enthusiasts' purist perspective".

Opinions a from non industry outsider !! We get calls regularly about HD programming and how to program their new TV Sets. True there are idiots out there who spend thousands on new TV sets, and still use them to watch SD programming, but there is also a large number of videophiles out there too, and these are the one MARIO is talking about.

What do you know about Mario? He has more years logged as a broadcast engineer than you have brain cells ! Why do you ALWAYS, ALWAYS, ALWAYS have to criticize someone you know nothing about? I would take the opinion of someone who has actually devoted their life to this industry than the opinion of someone who just likes to hear themselves think like you do.

This simple post exposes quite a bit about who you really are, and why you post here, and that is only to give yourself some type of twisted validation in life, and no, you don't know more about TV than MARIO !!

Contributor

And the loss of signals is not always the fault of the broadcasters. The FCC had a hard job of finding space for analog and digital to co-exist in a limited band. Power level assignments, market / signal overlap, and directional antennas all where considered in order to keep interference to a minimum.

A lot of stations still have, or had plans to improve their signal delivery infrastructure, but with the threat to the spectrum looming large, who wants to take a chance that that $250,000 you spent on an antenna or a transmitter upgrade won't just be thrown away at some point in the near future.

The digital transition is not over for a lot of stations, but who would spend money to upgrade a facility that may be off the air permanently in a few years. Until we have a definite direction in which to head in regards to the spectrum theft, no one will spend any money on major upgrades except for the big broadcast groups with deep pockets and plenty of tax write offs available to them.

DTVUSA Member

I agree with the article to an extent. WMAQ-TV is like a number of NBC O&O stations (only NBC O&O with NBC network on them, & not Telemundo) creating a Nonstop channel, & in the case of Chicago Nonstop, the picture quality looks horrible with blurriness & blocking with fast movements. Before Chicago Nonstop, it was a weather radar channel, & used less than 1mbps. Add to it, NBC O&O stations also have Universal Sports, & that uses bandwidth too. With the addition of Chicago Nonstop, bandwidth was taken away from both the HD NBC channel on 5.1, 5.3 Universal Sports, & bandwidth in reserve were added for 5.2. Now that additional bandwidth was taken away from Universal Sports 5.3, it looks even worse than before. It used to just look fuzzy. Now there's lots of blocking with fast movement, and lot of that with this channel. BTW, WMAQ-TV runs their HD in1080i.

WLS-TV is one of a few stations (also one of 8 ABC O&O) that runs 2 720p channels, with most of it allocated to the main channel 7.1. 7.2 is the Livewell Network, and ABC O&O stations (except for WJRT & WTVG, but these are being sold) run Livewell Network in HD. There's less bandwidth allocated to this channel, & it does block up with some quick movement. While this channel doesn't have as much fast movement, it does degrade the picture when any part of the picture moves fast. Then SD channel Accuweather on 7.3 doesn't really need that much bandwidth to it, but WLS-TV allocates around 1.2 (probably could go a little less than that) for Accuweather. While Livewell affiliates will run Livewell Network in SD, ABC O&O stations plan to continue with HD for this channel on their stations.

The only reason WBBM-TV looks great is because CBS O&O stations aren't allowed to have any subchannel (not even 1 subchannel), & they're 1080i.

While some people complain that WGN-TV looks horrible with their 1080i HD, but I see no problem with it, & they only run 1 subchannel. Right now, their subchannel is unmapped, & if you have a TV or converter box that can pickup unmapped channels, it's 19.4.

PBS station WTTW runs a 1080i HD channel, plus 3 SD subchannels. They program 11.1 & 11.2, but run the network feeds Create on 11.3 & V-Me on 11.4. 11.1 is the HD channel & is their general PBS programming & 11.2 is WTTW Prime, a 24 hour primetime program channel. While both channels look fine on a CRT TV, it looks blurry at times on an LCD TV. It looked somewhat better when WTTW was 720p. Since going back to 1080i, it looks terrible.

WCIU is one of those stations that somehow manages their bandwidth well enough that picture quality doesn't suffer too much. This station has the main channel in 720p (most programs are still SD, but they do carry some HD programming), while the other channels (all programmed in-house) are SD. The only channel that looks grainy is their channel, FBT on 26.6. I don't know how WCIU plans to fix that when they drop FBT & create U Too. Since WCIU's parent company is Weigel Broadcasting, they're also part owner of This TV, & that's also on WCIU. It looks ok. For those of you who complain about This TV not being Widescreen, blame Weigel & possibly MGM (most likely Weigel), because they wanted this channel to be 4:3 & not 16:9.

Do we even need to touch Ion Television? WCPX in Chicago looks horrible primarily because of the network feed of all 3 channels. It looks more like an analog picture than a digital picture.

Lastly, PBS station WYIN Gary Indiana is another station (the only one in the Chicago market) that runs 2 720p channels, but unlike WLS-TV, WYIN also runs 2 widescreen SD channels. All the channels look grainy. This station also simulcasts the main channel on 56.2 & 56.4, while they have their own PBS Kids Go channel on 56.3. Not sure when they'll put their remaining channels to good use. I wish they'd remove the 2nd HD channel & just run it in SD (keep it widescreen though for future use). They however have plans to add a 3rd HD channel when the technology improves. I can only see that happening if MPEG 4 is made available the ATSC standard.

Right now, Telemundo, Univision, & Telefutura run 1080i HD, & look great, even if Telemundo & Telefutura run only 1 HD channel & 1 SD channel. WFLD (Fox) for now doesn't have any subchannels, while sister station WPWR-TV (MNT) have some bandwidth set aside for Mobile TV, & have both WPWR-TV & WFLD on the mobile channel.

Based on just Chicago stations, cramming subchannels can work if done correctly. NBC, ABC, PBS stations WTTW & WYIN, & Ion Media (all Ion networks) do a poor job at managing subchannels & HD channel (HD channels for WLS-TV & WYIN) within their 6mhz channel. WCIU overall seems to do a much better job at managing their bandwidth on their station. I hear they do a good job on their Milwaukee station, WDJT, which is a CBS affiliate, & has an 1080i HD channel, plus 3 subchannels with This TV, a simulcast of lp station WMLW-CA (or is it LD), & a real estate channel. With any station Weigel Broadcasting owns, they move bandwidth around if any channel (particularly HD channels) need more bandwidth. They do it with WCIU when they air any sportscasts that get farmed out to them from WGN-TV.

The problem about complaints is that other signal providers have control over the quality of your signal on their individual systems meaning cable and satellite, unless you had quasi engineers helping write the re-transmission agreement. They should contain a clause about what mode (720P, 1080I, SD 480I or Letterbox, or Center cut, or Cropped, or full screen HD) that you want your signal rebroadcast in.

We had to force all of our cable affiliates to use letterbox so all viewers could see the entire picture content, and now we are getting complaints about the "Letterbox" format that is required for all of the old 4 X 3 displays to show the entire video frame, and lots of that people are still using older 4 X 3 Displays. If the complainers were cable viewers, I can see the basis for their complaints if they are on cable, as they are the biggest abusers of "Data Bit Thievery" that ultimately leads to signal resolution being lowered.

In order to make a fair comparison of video quality, you simply cannot compare cable or satellite programming to OFF AIR HD, or even OFF AIR SD, as the off air signal will win every time when comparing video resolution quality. OTA has the best picture period, but you don't see many people using that aspect of DTV broadcasting to promote FREE OTA HD. One HD stream be it 720P, or 1080I, along with one lower bit rate sub channel provides our station with error free and macro free signals.

We are a dual affiliate station with two transmitters with one being a 1080i CW outlet, and the other being a 720P FOX signal, and both of them have SD 480I sub channels being broadcast, and both are beautiful error free signals with no problems here except the mountainous area that we live in.

Moderator

And the loss of signals is not always the fault of the broadcasters. The FCC had a hard job of finding space for analog and digital to co-exist in a limited band. Power level assignments, market / signal overlap, and directional antennas all where considered in order to keep interference to a minimum.

A lot of stations still have, or had plans to improve their signal delivery infrastructure, but with the threat to the spectrum looming large, who wants to take a chance that that $250,000 you spent on an antenna or a transmitter upgrade won't just be thrown away at some point in the near future.

The digital transition is not over for a lot of stations, but who would spend money to upgrade a facility that may be off the air permanently in a few years. Until we have a definite direction in which to head in regards to the spectrum theft, no one will spend any money on major upgrades except for the big broadcast groups with deep pockets and plenty of tax write offs available to them.

Beyond a certain point though, using the same compression method, there comes a point where bitrate is the major factor. I wouldn't expect good 1080i HD quality below 10Mbps for example. It would be OK for many people, but even non-videophiles will find some overcompressed video simply awful. Then again, some of these people buy bootleg movies made from cam shots in movie theaters.

We get calls regularly about HD programming and how to program their new TV Sets. True there are idiots out there who spend thousands on new TV sets, and still use them to watch SD programming, but there is also a large number of videophiles out there too, and these are the one MARIO is talking about.

That's ridiculously childish. I am sorry that you're so afraid of losing your job that you feel compelled to blather on with silliness and refuse to acknowledge the reality that I'm outlining. Get over yourself little one.

DTVUSA Member

The goal, and what was achieved, as I recall, was actually around 98%, according to FCC documents. Still they did engineer the other 2% of viewers who had analog reception out of digital reception, as you suggest.

There can be issues with video content that can show up in digital video that have nothing to do with the transmitted signal strength, data issues etc. Take a noisy analog video and convert it to digital, and guess what...The noise also gets converted, and that can make you believe that it is a problem with the digital aspect or the data, when in reality, it was originally a converted noisy analog video (Video Noise) that is causing the picture to look noisy or degraded, but it is not related to the digital signal strength or the transmission method. Digital video DOES NOT DEGRADE as signal strength gets low until you get close to the noise floor of the receiver, and then you get macro blocking or signal drop out, but this is still not degradation of the video content, as it simply cannot degrade since it is nothing but 1's and 0's.

Contributor

Because any reasonable person would have presented it to support their case, if they went to the trouble.

No, but I'm a smart reasonable person. Are you?

As opposed to opinions biased by people saying whatever they think will save their own jobs?

Most households in the country now have an HDTV, but 80% of TV viewing in U.S. is still in standard definition, according to Nielsen. How are you going to try to equivocate yourself around that fact?

That's ridiculously childish. I am sorry that you're so afraid of losing your job that you feel compelled to blather on with silliness and refuse to acknowledge the reality that I'm outlining. Get over yourself little one.

The reality is that I do know, and deep-down you know it, and you are afraid. And so you lash out like a child against it. Grow up.

Look here Bitcher, I couldn't care less what you think in reality, I just like to point out how hung up you are on yourself and what you think you know. My life is really to busy right now to participate here as much as I have in the past, but when I see you criticize others because you think you know everything, then I have to respond. You are a sorry excuse for a human being, and if you put as much effort into actually being productive at something, instead of trying to show everyone how many uncommon and rarely used words you know we would all be better off on this forum.

No, but I'm a smart reasonable person. Are you?

Oh hell yes, I most certainly am a smart and reasonable person. Why do you think I hate the Democrats so much?

As opposed to opinions biased by people saying whatever they think will save their own jobs?

Look here Bitcher..I have other skills and I don't have to depend on this job. It is just that I like Broadcasting and things technical, and a free company vehicle to drive 24/7 helps a lot too. I have a degree in Computer Science too if I need a fallback skill ass face !!

Most households in the country now have an HDTV, but 80% of TV viewing in U.S. is still in standard definition, according to Nielsen. How are you going to try to equivocate yourself around that fact?

Ok Bitcher, this shows how little you really know. There is currently not enough HD content in existence right now to fill the needs of 24/7 broadcasters, unless you repeat a block of shows such as Discovery and the History channel do, and it is obvious that you are not aware of that fact, and your reliance on Nielsen for your facts and figures is one of the reasons you are wrong most all the time.

That's ridiculously childish. I am sorry that you're so afraid of losing your job that you feel compelled to blather on with silliness and refuse to acknowledge the reality that I'm outlining. Get over yourself little one.

That's no more childish than you thinking your opinion is always right and everyone else's is ALWAYS WRONG !! As stated before, this is not about my job from my point of view. This is about fairness and keeping Robber Barons from taking over another public resource for private profit.

The bottom line is that you are a complete ass face, and I doubt that even your mother really loves you. Yes, I have proven that I can be as childish as you, and you hate it when people use your own tactics against you. Grow up ass face. i despise you and your opinions, and that along with some new responsibilities in my life are the reasons i don't participate as much as I used to. It just gets boring to see your same old "I AM RIGHT AND I AM BETTER AND SMARTER THAN YOU, AND I KNOW ALL OF THESE RARELY USED WORDS THAT I CAN USE TO IMPRESS EVERYONE !!